Problem: $ { \left[\begin{array}{rr}{2} & {1} \\ {1} & {-1} \\ {3} & {1}\end{array}\right]-\left[\begin{array}{rr}{-2} & {4} \\ {-1} & {2} \\ {-1} & {-2}\end{array}\right] = {?} } $
To find the difference of two matrices, subtract the corresponding items between each matrix. ${\left[\begin{array}{rr}{2}-{-2} & {1}-{4} \\ {1}-{-1} & {-1}-{2} \\ {3}-{-1} & {1}-{-2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{4} & {-3} \\ {2} & {-3} \\ {4} & {3}\end{array}\right]}$